Adding a new CharLM model

Table of contents


For adding a new languages, we provide scripts to automate large parts of the process. Scripts for converting raw text to conllu and conllu to a charlm dataset can be found in stanza/utils/charlm/ and stanza/utils/charlm/

  • Gather a ton of tokenized text. Ideally gigabytes. Wikipedia is a good place to start for raw text, but in that case you will need to tokenize it.
    • One such source of text is the conll17 shared task
    • Another possibility is to gather the Common Crawl data yourself, such as from Oscar, and download the Wikipedia dump for the language
    • There is a script in the dev branch, stanza.utils.charlm.dump_oscar, which should help exporting Oscar data from HuggingFace to the charlm
  • If the data you gathered was from the conll17 shared task, we provide a script to turn it into txt files. Run python3 -m stanza.utils.charlm.conll17_to_text ~/extern_data/finnish/conll17/Finnish/ This will convert conllu or conllu.xz files to txt and put them in the same directory.
  • Run python3 -m stanza.utils.charlm.make_lm_data extern_data/charlm_raw extern_data/charlm This will convert text files in the charlm_raw directory to a suitable dataset in extern_data/charlm. You may need to adjust your paths.
  • Forward: python3 -m stanza.models.charlm --train_dir extern_data/charlm/fi/conll17/train --eval_file extern_data/charlm/fi/conll17/dev.txt.xz --direction forward --shorthand fi_conll17 --mode train
  • Backward: python3 -m stanza.models.charlm --train_dir extern_data/charlm/fi/conll17/train --eval_file extern_data/charlm/fi/conll17/dev.txt.xz --direction backward --shorthand fi_conll17 --mode train
  • This will take days or weeks to fully train.

For most languages, the current defaults are sufficient, but for some languages the learning rate is too aggressive and leads to NaNs in the training process. For example, for Finnish, we used the following parameters: --lr0 10

Step by Step Training

First, we need a large amount of text data. For this model, we choose two sources: Oscar Common Crawl and Wikipedia.

There is a script to copy Oscar from HuggingFace:

python3 -m stanza.utils.charlm.dump_oscar bn --output /nlp/scr/horatio/oscar/

We also download Wikipedia from the Wikipedia dumps archive. If a dump exists for your language, it will be under the language code for that language. We will use Prof. Attardiā€™s WikiExtractor tool to remove the markup, and it works on the latest-pages-meta-current file, so that is what we download.


You can then use the WikiExtractor to extract the text from the Wikipedia dump you just downloaded:

python -m wikiextractor.WikiExtractor bnwiki-latest-pages-meta-current.xml.bz2

This splits the text into multiple subdirectories full of small files AA, AB, ... depending on the size. The splits are smaller than we need, but we can combine them:

for i in `ls text`; do echo $i; cat text/$i/* > $i.txt; xz $i.txt; done

We now have an Oscar dump and a Wikipedia dump. We can turn this raw data into train/dev/test splits for the charlm. First, we organize the raw data into one directory. Then, we run the make_lm_data script. On our cluster, we put all of our raw charlm data into /u/nlp/software/stanza/charlm_raw and the train/dev/test splits into /u/nlp/software/stanza/charlm You can choose different base paths, of course.

export CHARLM_DIR=/u/nlp/software/stanza/charlm
export CHARLM_RAW_DIR=/u/nlp/software/stanza/charlm_raw
# move the Oscar & Wikipedia .xz files to this directory
mkdir -p $CHARLM_RAW_DIR/bn/oscar

ls $CHARLM_RAW_DIR/bn/oscar
AA.txt.xz  oscar_dump_000.txt.xz  oscar_dump_007.txt.xz  oscar_dump_014.txt.xz  oscar_dump_021.txt.xz
AB.txt.xz  oscar_dump_001.txt.xz  oscar_dump_008.txt.xz  oscar_dump_015.txt.xz  oscar_dump_022.txt.xz
AC.txt.xz  oscar_dump_002.txt.xz  oscar_dump_009.txt.xz  oscar_dump_016.txt.xz  oscar_dump_023.txt.xz
AD.txt.xz  oscar_dump_003.txt.xz  oscar_dump_010.txt.xz  oscar_dump_017.txt.xz
AE.txt.xz  oscar_dump_004.txt.xz  oscar_dump_011.txt.xz  oscar_dump_018.txt.xz
AF.txt.xz  oscar_dump_005.txt.xz  oscar_dump_012.txt.xz  oscar_dump_019.txt.xz
AG.txt.xz  oscar_dump_006.txt.xz  oscar_dump_013.txt.xz  oscar_dump_020.txt.xz

python3 -m stanza.utils.charlm.make_lm_data $CHARLM_RAW_DIR $CHARLM_DIR --langs bn --packages oscar

You can now run the charlm. This will take days. Remember to update the language!

python3 -m stanza.models.charlm --train_dir $CHARLM_DIR/bn/oscar/train --eval_file $CHARLM_DIR/bn/oscar/dev.txt.xz --direction forward --shorthand bn_oscar --mode train > bn_forward.out 2>&1 &
python3 -m stanza.models.charlm --train_dir $CHARLM_DIR/bn/oscar/train --eval_file $CHARLM_DIR/bn/oscar/dev.txt.xz --direction backward --shorthand bn_oscar --mode train > bn_backward.out 2>&1 &

You can tell when the model has converged and is no longer improving by looking for the eval scores:

grep "eval checkpoint" bn_*.out

Alternatively, you can tie it in to wandb (requires Stanza 1.4.1 or later) by signing in to wandb and adding wandb_name to the original command line:

python3 -m stanza.models.charlm --train_dir $CHARLM_DIR/bn/oscar/train --eval_file $CHARLM_DIR/bn/oscar/dev.txt.xz --direction forward --shorthand bn_oscar --mode train --wandb_name bn_oscar_forward_charlm > bn_forward.out 2>&1 &
python3 -m stanza.models.charlm --train_dir $CHARLM_DIR/bn/oscar/train --eval_file $CHARLM_DIR/bn/oscar/dev.txt.xz --direction backward --shorthand bn_oscar --mode train --wandb_name bn_oscar_backward_charlm > bn_backward.out 2>&1 &

Once it has converged satisfactorily, you can copy the models to the expected locations in your stanza resources and rerun the NER. If you follow the name structure used in this example command line, will look for and find the charlm in these exact paths. Remember that you can update $STANZA_RESOURCES_DIR if you need.

mkdir -p ~/stanza_resources/bn/forward_charlm
cp saved_models/charlm/ ~/stanza_resources/bn/forward_charlm/

mkdir -p ~/stanza_resources/bn/backward_charlm
cp saved_models/charlm/ ~/stanza_resources/bn/backward_charlm/

python3 -m bn_daffodil --charlm oscar --save_name

Integrating with other models

Once the charlm is trained, you can integrate it to NER as follows. Other models which support charlm are similar.

mkdir -p ~/stanza_resources/bn/forward_charlm
cp saved_models/charlm/ ~/stanza_resources/bn/forward_charlm/

mkdir -p ~/stanza_resources/bn/backward_charlm
cp saved_models/charlm/ ~/stanza_resources/bn/backward_charlm/

python3 -m bn_daffodil --charlm oscar --save_name


Akbik, Alan and Blythe, Duncan and Vollgraf, Roland. Contextual String Embeddings for Sequence Labeling, Proceedings of the 27th International Conference on Computational Linguistics, Association for Computational Linguistics, 2018.